structure FEATURE support for ietf-yang-structure-ext

Only for the structure itself, no augment yet.
diff --git a/src/plugins_exts/structure.c b/src/plugins_exts/structure.c
new file mode 100644
index 0000000..781cde0
--- /dev/null
+++ b/src/plugins_exts/structure.c
@@ -0,0 +1,214 @@
+/**
+ * @file structure.c
+ * @author Michal Vasko <mvasko@cesnet.cz>
+ * @brief libyang extension plugin - strcture (RFC 8791)
+ *
+ * Copyright (c) 2022 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libyang.h"
+#include "plugins_exts.h"
+
+struct lysc_ext_instance_structure {
+    struct lysc_must *musts;
+    uint16_t flags;
+    const char *dsc;
+    const char *ref;
+    struct lysp_tpdf *typedefs;
+    struct lysp_node_grp *groupings;
+    struct lysc_node *child;
+};
+
+/**
+ * @brief Compile structure extension instances.
+ *
+ * Implementation of ::lyplg_ext_compile_clb callback set as lyext_plugin::compile.
+ */
+static LY_ERR
+structure_compile(struct lysc_ctx *cctx, const struct lysp_ext_instance *p_ext, struct lysc_ext_instance *c_ext)
+{
+    LY_ERR ret;
+    LY_ARRAY_COUNT_TYPE u;
+    struct lysc_module *mod_c;
+    const struct lysc_node *child;
+    struct lysc_ext_instance_structure *struct_ext;
+    uint32_t prev_options = *lysc_ctx_get_options(cctx);
+
+    /* structure can appear only at the top level of a YANG module or submodule */
+    if ((c_ext->parent_stmt != LY_STMT_MODULE) && (c_ext->parent_stmt != LY_STMT_SUBMODULE)) {
+        lyplg_ext_log(c_ext, LY_LLERR, LY_EVALID, lysc_ctx_get_path(cctx),
+                "Extension %s must not be used as a non top-level statement in \"%s\" statement.",
+                p_ext->name, ly_stmt2str(c_ext->parent_stmt));
+        return LY_EVALID;
+    }
+
+    mod_c = (struct lysc_module *)c_ext->parent;
+
+    /* check identifier namespace */
+    LY_ARRAY_FOR(mod_c->exts, u) {
+        if ((&mod_c->exts[u] != c_ext) && (mod_c->exts[u].def == c_ext->def) && !strcmp(mod_c->exts[u].argument, c_ext->argument)) {
+            /* duplication of the same structure extension in a single module */
+            lyplg_ext_log(c_ext, LY_LLERR, LY_EVALID, lysc_ctx_get_path(cctx), "Extension %s is instantiated multiple times.", p_ext->name);
+            return LY_EVALID;
+        }
+    }
+    LY_LIST_FOR(mod_c->data, child) {
+        if (!strcmp(child->name, c_ext->argument)) {
+            /* identifier collision */
+            lyplg_ext_log(c_ext, LY_LLERR, LY_EVALID, lysc_ctx_get_path(cctx), "Extension %s collides "
+                    "with a %s with the same identifier.", p_ext->name, lys_nodetype2str(child->nodetype));
+            return LY_EVALID;
+        }
+    }
+
+    /* allocate the storage */
+    struct_ext = calloc(1, sizeof *struct_ext);
+    if (!struct_ext) {
+        goto emem;
+    }
+    c_ext->data = struct_ext;
+
+    /* compile substatements */
+    LY_ARRAY_CREATE_GOTO(cctx->ctx, c_ext->substmts, 14, ret, emem);
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[0].stmt = LY_STMT_MUST;
+    c_ext->substmts[0].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[0].storage = &struct_ext->musts;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[1].stmt = LY_STMT_STATUS;
+    c_ext->substmts[1].cardinality = LY_STMT_CARD_OPT;
+    c_ext->substmts[1].storage = &struct_ext->flags;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[2].stmt = LY_STMT_DESCRIPTION;
+    c_ext->substmts[2].cardinality = LY_STMT_CARD_OPT;
+    c_ext->substmts[2].storage = &struct_ext->dsc;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[3].stmt = LY_STMT_REFERENCE;
+    c_ext->substmts[3].cardinality = LY_STMT_CARD_OPT;
+    c_ext->substmts[3].storage = &struct_ext->ref;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[4].stmt = LY_STMT_TYPEDEF;
+    c_ext->substmts[4].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[4].storage = &struct_ext->typedefs;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[5].stmt = LY_STMT_GROUPING;
+    c_ext->substmts[5].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[5].storage = &struct_ext->groupings;
+
+    /* data-def-stmt */
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[6].stmt = LY_STMT_CONTAINER;
+    c_ext->substmts[6].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[6].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[7].stmt = LY_STMT_LEAF;
+    c_ext->substmts[7].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[7].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[8].stmt = LY_STMT_LEAF_LIST;
+    c_ext->substmts[8].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[8].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[9].stmt = LY_STMT_LIST;
+    c_ext->substmts[9].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[9].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[10].stmt = LY_STMT_CHOICE;
+    c_ext->substmts[10].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[10].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[11].stmt = LY_STMT_ANYDATA;
+    c_ext->substmts[11].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[11].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[12].stmt = LY_STMT_ANYXML;
+    c_ext->substmts[12].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[12].storage = &struct_ext->child;
+
+    LY_ARRAY_INCREMENT(c_ext->substmts);
+    c_ext->substmts[13].stmt = LY_STMT_USES;
+    c_ext->substmts[13].cardinality = LY_STMT_CARD_ANY;
+    c_ext->substmts[13].storage = &struct_ext->child;
+
+    *lysc_ctx_get_options(cctx) |= LYS_COMPILE_NO_CONFIG | LYS_COMPILE_NO_DISABLED;
+    ret = lys_compile_extension_instance(cctx, p_ext, c_ext);
+    *lysc_ctx_get_options(cctx) = prev_options;
+    if (ret) {
+        return ret;
+    }
+
+    return LY_SUCCESS;
+
+emem:
+    lyplg_ext_log(c_ext, LY_LLERR, LY_EMEM, lysc_ctx_get_path(cctx), "Memory allocation failed (%s()).", __func__);
+    return LY_EMEM;
+}
+
+/**
+ * @brief INFO printer
+ *
+ * Implementation of ::lyplg_ext_schema_printer_clb set as ::lyext_plugin::sprinter
+ */
+static LY_ERR
+structure_schema_printer(struct lyspr_ctx *ctx, struct lysc_ext_instance *ext, ly_bool *flag)
+{
+    lysc_print_extension_instance(ctx, ext, flag);
+    return LY_SUCCESS;
+}
+
+/**
+ * @brief Free structure extension instances' data.
+ *
+ * Implementation of ::lyplg_clb_free_clb callback set as lyext_plugin::free.
+ */
+static void
+structure_free(struct ly_ctx *ctx, struct lysc_ext_instance *ext)
+{
+    lyplg_ext_instance_substatements_free(ctx, ext->substmts);
+    free(ext->data);
+}
+
+/**
+ * @brief Plugin descriptions for the structure extension
+ *
+ * Note that external plugins are supposed to use:
+ *
+ *   LYPLG_EXTENSIONS = {
+ */
+const struct lyplg_ext_record plugins_structure[] = {
+    {
+        .module = "ietf-yang-structure-ext",
+        .revision = "2020-06-17",
+        .name = "structure",
+
+        .plugin.id = "libyang 2 - structure, version 1",
+        .plugin.compile = structure_compile,
+        .plugin.sprinter = structure_schema_printer,
+        .plugin.free = structure_free,
+        .plugin.node = NULL,
+        .plugin.snode = NULL,
+        .plugin.validate = NULL
+    },
+    {0}     /* terminating zeroed record */
+};